Data from fossil toe bone points to surprising interbreeding among early humans.

Data obtained from a Neanderthal woman's toe bone points to incest and inbreeding among early humans, an international genetics team reported on Wednesday.

The fossil's genetic map, or genome, reported from Denisova cave in Siberia's Altai Mountains dates to more than 50,000 years ago. The cave was home at separate times to both Neanderthals and the so-called Denisovans, two sister families of now-extinct early humans. (See also "New Type of Ancient Human Found.")

Adding to increasing evidence of a tangled human family tree, the new Neanderthal genome study released by the journal Nature also suggests that another previously unknown archaic human species shared its genes with some of our ancestors. The study authors suggest that it was Homo erectus, one of the earliest human species, which first arose around 1.8 million years ago. (See also "Why Am I a Neanderthal?")

The report, led by Germany's Kay Prüfer of the Max Planck Institute for Evolutionary Anthropology in Leipzig, builds on recent prehistoric genetics results that argue against theories that modern humans arose completely from one "out of Africa" migration more than 60,000 years ago that spread worldwide without mating with other early humans.

Instead, it looks like early modern humans sometimes mated with archaic human cousins they met along the way. People of non-African origin broadly have genes that are 1.5 percent to 2.1 percent Neanderthal, according to the study, with proportions higher among Asians and Native Americans. Similarly, 5 percent of the genome of people of Australian and Papua New Guinea descent looks Denisovan, as does 0.2 percent of the genes of people from Asia.

"We don't have one ancestral group, but proportions of ancestral groups," says computational biologist Rasmus Nielsen of the University of California, Berkeley, who was not part of the study team. "I think they make a convincing argument."

"In my view, this paper heralds the completion of the Neanderthal genome project in terms of mapping an entire genome," says paleontologist and human origins expert Richard Potts of the Smithsonian's National Museum of Natural History in Washington, D.C. "That's pretty cool science."

Kissing Cousins

In 2010, the study's toe bone first turned up at Denisova Cave, where excellent fossil preservation conditions had allowed for the genetic mapping of the then-surprising Denisovan finger bone found in 2008. Gene tests showed the toe belonged to a Neanderthal, and Prüfer and colleagues began calculating its full genetic map.

Photograph by B. Viola, MPI f. Evolutionary Anthropology

The dorsal view of the Denisova Neanderthal toe bone is shown.

The results show that it belonged to a woman whose closely matched chromosomes suggest that her parents were closely related, perhaps half-siblings or an uncle and niece (or aunt and nephew).

This incest finding "is more of an anecdote," says evolutionary biologist Mattias Jakobsson of Sweden's Uppsala University, who was not part of the study. "The more interesting observation would be if this mating behavior was common among Neandertals and/or Denisovans compared to [early modern humans] at that time," he said by email.

Over time, such inbreeding has been shown to be bad for the genetic fitness of most species, including people, throughout the animal world.

Comparison of the Neanderthal genome with a previously sequenced Denisovan one shows that both early species were far more limited, scattered, and isolated than early modern humans.

The study raises the possibility that both species were on their way to going extinct before early modern humans arrived on the scene.

Better Genes Borrowed

The findings suggest that Neanderthals and Denisovans split off from earlier human species around 600,000 years ago and split from each other perhaps 400,000 years ago.

The accuracy of the Neanderthal genome actually allows the researchers to proclaim that the Neanderthal found in Denisova Cave is less closely related to modern people than to a Neanderthal found at a site in the Caucasus.

Only 96 genes responsible for making proteins in cells are different between modern humans and Neanderthals. Intriguingly, some of the gene differences involve ones involved in both immune responses and the development of brain cells in people.

More Ancient Ancestor

"The suggestion of gene flow from Homo erectus to Denisovans is also interesting," says Potts. "I think the evidence of this event is mounting."

In the study, the authors report their evidence from a deep comparison of the new Neanderthal genome and the Denisovan one.

While Denisovans are more closely related to Neanderthals than modern humans are, as much as eight percent of their total genome comes from a "super archaic" (in Prüfer's words) early human species at least 900,000 years old, most likely Homo erectus.

"The promise of vastly growing knowledge about what distinguishes people today from Neanderthals, and other extinct cousins, mirrors people's interest in what makes them tick and what they pass on genetically," Potts says.

"Frankly, I'm delighted by the idea that people can begin to think about themselves as connected to other species, extinct smart bipeds different from themselves."

The only thing that prevented more crossbreeding in ancient times was their archaic transportation system and the inability to travel very far, even in a lifetime, however now with our mass worldwide transportation system we will rapidly be seeing all of the different nationalities and tribes interbreed. It won't be too long in the future until all people on earth are of the same appearance. We will have come full circle and back to Babylonian
times when all humans spoke the same language and were one. Will that be good or bad...I don't know.

The small and scattered communities of the Neanderthals and Denisovans would have made it hard to breed in a more diverse gene pool. It is not uncommon with prehistoric people to mate with ones sister, brother, cousin. Limited options cause this out of necessity. However, I do believe that it led to a downfall in the population due to the problems with interbreeding within one's close family. Weaker offspring, early childhood deaths, miscarriages. Without the diversity of other gene pools, you come up with many problems which can lead to extinction.

This is a great article but it is frustrating that so many reputable publishers are still making a large error by still going along with Max Planck institute's outdated (proven inaccurate) conclusion that says that modern humans may have mated with Neanderthal's and other separate species, such as Denisovans. At this point that outdated info is charging up into a myth-hype that overshadows the careful science we are use to in these articles. After Dr. Paabo's inaccurate assertion, a study was published in PNAS in August of 2013 by Dr Andrea Manica of Cambridge University that proved that this notion of interbreeding between species had no sound basis and was unlikely because, as further illuminated by this article, many groups within the same species have closer or more distantly shared ancestry with relative species. If one group has more shared genes than another group, it doesn't always mean that radically different and separate species had babies with one another, duh. This fits other new research that pushes our divergence from Neanderthal all the way back to nearly 1 million years ago which means different groups of modern humans or an undiscovered intermediate species or both were evolving in Africa for a long time prior to the new Omo 1 fossil date of 195,000 bp. Also, prompted by improved and more accurate dating techniques used for Idaltu Man and then used to change Omo fossil dates, researchers from UNED published a study in Feb 2013 that re-dated Neanderthal fossils and showed they actually died out 50,000 years ago, not 30,000, thus eliminating the opportunity for interbreeding. It is very important to correct this mistake instead of the letting this tabloid-style, melodrama continue and that might as well be about deviant sex between chimps and baboons given the scientific support and significance of these assertions. It only distracts from the exciting changes that are rapidly and radically expanding our understanding of ourselves in the context of other species of humans, thanks to Dr Paabo and the like. The alternative explanations are incredibly exciting. Dr Aida Gomez-Robles at George Washington University published in PNAS in October 2013 to show that our common ancestor with Neanderthal diverged possibly further than 900,000 years ago, not 3 to 4 hundred thousand years ago and showed that Neanderthal's teeth confirmed she was very distant relative despite our seeming similarities and shared genes, and that there must be another, undiscovered transitional species between ourselves and our common ancestor with Neanderthal. We can overcome big obstacles facing us today if we better understand who we are, our limitations and advantages, by sharpening our understanding of who they are. Although the multi-regional/multi-species orgy enthusiast might disagree, we cannot ignore important and well founded pieces of the puzzle just because it doesn't support what we want to be true.

With the limited numbers found so far of Denisovan and Neanderthal bones, it looks like their communities may have been quite small and scattered. With only transportation on foot at their disposal(no ancient chariots or horse bones found with the hominids bones), it seems unlikely that individuals at the time had a lot of mating options other than inbreeding open to them. Probably why they were already on their way out. Also contributing could be in groups that practiced cannibalism you would also likely have some kind of ancient "Mad Cow" type neurological degeneration.

If we look at the history of Latin America, specially South America, we can see the same thing. When the Europeans, not only Spanish and Portuguese, but also Germans, Irish and others, emigrated to South America in the 1600's, the man left Europe first. Once in South America, they took a common law wife of indian or african ancestry or both, while waiting from their European wife. When the man was settled, the European wife arrived. So, the same man, may have three set of children: 100%European Blood, 50% indian & 50% European, and 50% african and 50% European. It was not considered at that time to be unfaithfull to take a second or third wife.

In some countries, children out of wedlock will inherit 25% of the property and legitimate children 75%.

Geneticists have found lots of evidence of inbreeding in human populations too, leading to a fierce debate among genetic anthropologists about whether a genetic "bottleneck" occurred somewhere in the last 100,000 years or so. By a genetic bottleneck, they mean a huge reduction in human population size, resulting in massive inbreeding. Some very well known geneticists have argued this occurred and kept going for a pretty long time, beginning around 70,000 years ago.

John Hawks, an anthropologist I like because he writes well and I can understand what he says, argues they lack they evidence to show a species wide bottleneck because he can't find enough anomalies throughout the species.

But that brings up an interesting point. If humans had a genetic bottleneck (at least in some areas of the world) and neanderthals had one, did something seriously bad happen to the whole planet? Like a giant meteor strike? Did various human species interbreed by choice, or by necessity?

Interesting! "The study raises the possibility that both species were on their way to going extinct before early modern humans arrived on the scene" This may not be true, since the cave dates 50,000 years ago which is 10,000 years later after modern human expanded to Eurasia. Neanderthals might have to inbreed because they were almost extinct.

I did start my comment with "If". Anyway no one knows the absolute answer to where we came from its all speculation based on either faith or science. I will only be convinced if a spirit creature appeared to all people and told us the truth or if an explorer found a cave full of frozen fish with legs or a frozen half human half ape. Even more interesting a frozen Alien from who knows where.

If Adam and Eve were the original first humans it makes sense that incest was a fact of life at the beginning because their children would have had to interbreed with each other until there were enough other humans to go around.

@Gabriele Menefee Can you cite your source material on your claim that "It is not uncommon with prehistoric people to mate with ones sister, brother, cousin."? I would be interested to read that information because I had never heard of such a thing being common.

@Maria OConnor i agree with you on that however lets not be to light on the percantages ,,, we dont inherit 50-50 from parents,, that the beauty of evolution,, we grab the supposely better genes,, anyhow, since in a sense we are all related,, it doesnt matter your backgroung somewhere along the lien our ancestors crossed path,, making us ralted,,,let say native american have a child with an european,, of course the baby will have traces of both parents but sence we all share as humans the same gens,, the child is 100% human and will have some natives and european features,, not the 50%, or whatever,, it just a fallacy when people claim i am 1/8 native american or whatever %,,, and nowadays those dna that supposely tell you whats up its a gimmick to make money,,just think how many grandparents you have and so on ....and then they tell you something like this,. " well for sure as for where your dna stand, 500 hundred years ago,, your family where located in this part of the globe or you come from this region,, they analize a small fraction of your dna but if you know how the dna goes,, they fallow your moms moms and her moms moms and so on,,,and do the same on your father,, and lets say,, they manage to go back 20 generation or 30,,,, so technically they follow 30 back from each side,,, now the question is how many great grandparents have they missed?,, take a wild high guess,,, junt on 14 generatrions back lets say year 1600,, youll have 16,384 grandparents,,related directly to you,,,, you see my point,, i think the stronger outlived the others by either mixing or by the others interbreeding limited their chances to evolve,, and therefore extint,,

@Tom CarberrySomething bad did happen, but not to the whole planet. The Toba volcano in Sumatra exploded about 74,000 years ago, considered the biggest eruption of the last 2 million years, and caused a prolonged nuclear winter releasing ash in a huge plume that spread to the north-west and covering India, Pakistan and the Gulf region in a blanket 1-3 metres deep.

This would have resulted in the near extinction of any humans who had occupied the Indian sub-continent, leaving a deep east-west division, or "furrow", which is still clearly seen in the genetic record.

"speculation based on either faith or science" Speculation on faith is meaningless whereas speculation based on science is called hypothesizing and it lead to space travel, the computer and the theory of evolution.

I was thinking the same thing. It requires a bottleneck according to Darwin for a separate species to arise, just from this inbreeding mechanism. A population of a species becomes separated from the rest, just long enough in some cases to create variation, the incest causes evolutionary diversication for those "set apart" organisms. It disrupts the hereditary process in some way, possibly adding some discordant notes.

@Omar Aboelfetouh this proves nothing of the sort anyways, Eve wasn't the first woman on earth, your precious Adam was married first to Lilith, but supposedly she was unruly and disobedient, so god gave him a second wife. and that could be where divorce was created??? hmmm?

@Omar Aboelfetouh Better the Darwin ! Except that his theory rests on a life of research and thousands of pages and your in some pages in improbable papers. You Dont know the consequences of the consanguinity ? Type "Maison de Habsbourg en Espagne" in the French Wikipedia and read the section "Consanguinité des Habsbourg" (use reverso if you need it). Later it gives a being as sick and especially sterile Charles II of Spain, it is impossible that the humanity arises from a single couple. You'll maybe have a change of mind but I do not believe in it, the faith blinds.

@gavin o The Bible clearly says there was incest up to the time of Moses. He made incest illegal by the command of God for the very reason that incest was no longer needed to populate the human race. We are all (Muslims and Atheists included) children of Abraham whose wife was his half sister.

Maybe, but maybe not. A lot of scientist raise the Toba theory to explain the population declines. The arguments don't convince me, because we have no human mythology to support such an event.

By contrast, every human society has mythology about bad things coming from the sky. The Greeks believed (as did the Hittites before them) that Jupiter destroyed his father Chronos, and then ejected Venus from his shoulder.

Such sky god war myths exist around the world.

For many years scientists have posited a steady state solar system, that worked on a nice steady revolutions. But even a glance at the moon disproves this theory.

If in fact major problems in the solar system occurred thousands of years ago and continued to occur for a long time, that would explain a lot of the myths and explain the population decline.

We don't know one way or the other yet.

But the solar system offers a lot of questions. When did the asteroid belt come into existence? Long ago, or within human memory? Did Chronos orbit there? Or why does Venus have a retrograde revolution? What happened to Mars's atmosphere and when? Millions of years ago, or a few thousand years ago?

@Ray M. No. We are all the descendants of " proteinoids microspheres " of peptides existing on Earth there is more than 3 billion years. What do you come all to make on this scientific site to part refute indisputable proofs with how arguments of manuscripts indatables and faith? Let's go we safe your sites to provoke you? No